1. Field of the Invention
The present invention relates to an apparatus for measuring transmittance, and more particularly, to an apparatus for measuring the transmittance of a piece of patterned glass, in which reliability for measurement of the transmittance of the patterned glass can be achieved by post dispersion of light.
2. Description of Related Art
Recently, as a counter measure to the shortage of energy resources and environmental pollution, the development of photovoltaic modules is underway on a large scale. The efficiency of photovoltaic modules is influenced by the transmittance of a piece of cover glass. Accordingly, an enormous amount of research and development is underway in order to improve the transmittance of the cover glass, for example, by minimizing the internal absorption ratio using a composition of the cover glass or improving the transmittance using a coating. In addition, in order to improve the transmittance of the cover glass, a piece of patterned glass is formed by imparting a two-dimensional (2D) array pattern on a light incident surface of the cover glass. The patterned glass is being widely used not only for photovoltaic modules, but also for flat panel display devices.
Glass substrate manufacturers conduct real-time precise inspection of the transmittance of a piece of patterned glass which is continuously produced by directing light into the glass during the process in which the patterned glass is being manufactured.
A spectrometer is an apparatus of the related art which is used for measuring the transmittance of a piece of patterned glass. As shown in FIG. 1 and FIG. 2, the spectrometer of the related art is configured as an optical system which includes a light source 11, a light dispersing device 12, an integrating sphere 13 and a detector 14. The ISO 9050 international standards regulate that the transmittance of a glass substrate G with respect to solar light be calculated by respectively multiplying spectral transmittances with weighted spectral sensitivities of a measuring system with respect to a standard light source D65 which is used for measurement. Accordingly, the spectrometer of the related art is realized such that it can represent spectral transmittances of visible light in the range from 380 nm to 780 nm by receiving all of the light and then processing the received light. That is, all spectral transmittances for an object of interest are required in order to measure the transmittance of the glass substrate G using the spectrometer of the related art.
As shown in FIG. 3, for a piece of patterned glass, when light is received using the fixed detector, an accurate transmittance cannot be measured since the light greatly diffuses after it has passed through the patterned glass. This is because, in some cases, when incident light that has passed through the patterned glass G greatly diffuses, the detector 14 fixed to the integrating sphere 13 fails to receive the light, as shown in (a) of FIG. 3. Here, (b) of FIG. 3 shows the shape of a laser beam that has diffused after having passed through a piece of non-patterned glass in order to compare it with (a) of FIG. 3, i.e. the result of the patterned glass.
Therefore, when the transmittance of a piece of patterned glass is measured using a spectrometer of the related art, there is the problem of the unreliability of results. As shown in FIG. 4, this is because the intensity of light that is received by the fixed detector 14 may have a measurement error, attributable to different spectral angles of emergence into the air. In particular, for the patterned glass, angles of emergence have a wide distribution attributable to severe scattering of light that has passed through the patterned glass, leading to different integration paths and aspects depending on wavelengths. Therefore, the possibility that the fixed detector 14 may have an error in the measurement of the intensity of light that it has received is further increased. Specifically, in order to increase the transmittance, a piece of cover glass for crystalline photovoltaic cells has a pattern in the upper surface thereof which reduces reflection and increases the intensity of transmission light. When the cover glass for photovoltaic cells which has this pattern, i.e. the patterned glass, is measured using the spectrometer of the related art which receives light after dispersing it, the transmittance cannot be measured accurately, and the high-transmittance effect of the patterned glass cannot be verified.
FIG. 5 is a graph showing the result of transmittance measurement on a piece of high-transmittance patterned glass using an apparatus for measuring transmittance of the related art. Although the transmittance of the patterned glass was measured to be 87.5%, its simulated transmittance was about to be 92.3%. In addition, as shown in FIG. 6, when a piece of patterned glass G was measured using direct transmission, its transmittance with respect to a mixture of wavelengths was measured about 92.46%. Thus, it can be appreciated that a measurement error occurs when the transmittance of the patterned glass G is measured using the spectrometer of the related art.
However, the approach for measuring transmittance using direct transmission shown in FIG. 6 has a drawback in that spectral transmittances are not obtained. Thus, this approach has a limited ability as an apparatus for determining spectral transmittances of the patterned glass.
Accordingly, the apparatus for measuring transmittance of the related art is apparently limited in its ability for reliably measuring the spectral transmittances of the patterned glass.
The information disclosed in the Background of the Invention section is only for the enhancement of understanding of the background of the invention, and should not be taken as an acknowledgment or any form of suggestion that this information forms a prior art that would already be known to a person skilled in the art.